System_Command is a commandline execution interface. Running functions
from the commandline can be risky if the proper precautions are not
taken to escape the shell arguments and reaping the exit status
properly. This class provides a formal interface to both, so that you
can run a system command as comfortably as you would run a php function,
with full pear error handling as results on failure. It is important to
note that this class, unlike other implementations, distinguishes
between output to stderr and output to stdout. It also reports the exit
status of the command.
